Peat moss belongs to the genus sphagnum and is a plant that grows from the top while the bottom part dies and changes into peat. Chemically, peat moss consists of about 50%, by weight, lignin and humic acid with the remainder consisting of hemicellulose, cellulose, waxes and nitrogen compounds. Physically, peat moss leaf is one cell layer thick, the cells having thin, lignified walls. The cells or pores of the leaflike structure are generally evenly distributed about the surface of the leaf and range in size from about 15 to 40 microns in diameter. It is on the surface and on the walls of the pores that the lignin is primarily distributed and as a result, the peat exhibits a dark brown to yellow color.
Primarily because of the pore structure, peat moss has the ability to absorb and hold relatively large amounts of water within the capillaries formed by the pores, and so has found considerable use in the horticultural industry. Additionally, peat moss has been used in water treatment techniques.
It has also been suggested by various prior investigators that peat moss be used as an absorbent dressing for body fluids in such products as sanitary napkins, tampons, or diapers. Such use, however, has not found wide acceptance and it is believed that this lack of acceptance is related to the problem of color, i.e., the consumer or user does not like the unduly dark color of peat moss.
While many processes exist for bleaching lignin, particularly lignin found in wood pulp, it is believed that no such prior process could produce a peat moss product which has the satisfactorily high brightness to suit consumer preferences. One achievement in this direction is described in a commonly assigned patent application filed in the U.S. Pat. and Trademark Office in Feb. 21, 1978 as Ser. No. 879,833, now U.S. Pat. No. 4,170,515 by Drs. Jean-Marc Lalancette and Bernard Coupal. In accordance with that application, peat moss may be bleached, using a bleaching process which takes place under acid conditions, to obtain structurally integral product having a color level on the Hunter Scale of up to about 75. Unfortunately, when attempts are made to increase the severity of the bleaching process or prolong the process in an effort to obtain still whiter peat moss, the structural integrity of the product is destroyed, the leaf collapses and the structure creating the capillaries responsible for the absorptive properties of the peat moss disappears. The reason for this is believed to be that the same lignin and humic acid, disposed on the surface of the leaf, which gives peat moss its dark color also prevents the peat moss from collapsing and is responsible for the property of maintaining capillary structure when wet. To bleach peat moss brighter in color than about 75 on the Hunter Scale requires removal of the lignin which, in turn, causes the undesirable collapse of the peat moss structure. Accordingly, bright absorbent peat moss and a method for making the same has heretofore eluded the art.